I was bored and I looked at Fields's stats now that the season is over and... While I think, from the eye-test, he was better as a passer this year, his numbers are virtually identical to last year.
The Yards Per Attempt are nearly the same, the adjusted Y/A are identical, the Yards Per Catch are identical, the success rate is just a tick higher. The TD% is slightly lower, the INT% is down a percentage.
He averaged 50 more yards a game but thats more of a function of throwing more, not more efficiently.
The only number that changed significantly is he cut his Sack rate down by 4%, but its still way too damn high.
I think its very hard to justify passing on a QB given these numbers.